This invention relates to electronic surveillance systems, and particularly to surveillance systems designed and adapted to probe optical systems in a remote vehicle, such as a weapon or an Earth-orbiting artificial satellite.
In the prior art there have been known systems, generally designated "optical augmentation systems" for transmitting a light beam, preferably a laser beam, with concentrated intensity in the direction of a suspected non-friendly optical system, such as a laser rangefinder on an artillery weapon, a surveillance camera, or a periscope. The basic characteristic of typical focal plane optics, including cameras, TV vidicons, telescopes, photomultiplier tubes, and rangefinders, is that radiation incident on the detecting instrument, which originates within the field-of-view of the detecting instrument, tends to be retro-reflected in a concentrated beam in the direction from which it was incident. Thus, a laser beam directed at a non-friendly satellite with camera surveillance equipment is focused onto the image plane of the camera equipment, reflected off the smooth surface of the image plane, refocused into a concentrated retro-reflected beam by the lens of the camera equipment and retransmitted from the camera in the direction from which it was incident.
By making use of this retro-reflection characteristic of optical systems, including non-friendly optical systems, it becomes possible to detect and track such optical systems and to determine certain characteristics of the optical equipment, and thereby obtain information regarding the type of equipment which is included in a non-friendly vehicle, such as a satellite, a ship, or an armored vehicle.
One difficulty with prior art optical augmentation systems using laser illumination is that an enemy vehicle may sense the fact that it is being illuminated by laser light. Laser light is easily sensed because it has discrete frequency ranges, which are determined by the type of laser being used. By detecting the emission of laser light from an installation, an enemy vehicle can sense that it is being illuminated by a laser. This determination can be provocative to the owner or operator of the vehicle and the incident laser beam can be used for determining the location of a military installation or friendly equipment.
It is therefore an object of the present invention to provide an optical augmentation system which is capable of probing a non-friendly vehicle or equipment without alerting the owner of the vehicle or equipment to the fact that such probing is taking place.
Is is a further object of the present invention to provide a non-provocative illumination source for photography
It is a still further object of the present invention to provide non-provocative means for inhibiting operation of non-friendly optical equipment.